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Dementia, a syndrome with many causes, affects >5 million people in the United States and results in a total annual health care cost between $157 and $215 billion. Dementia is defined as an acquired deterioration in cognitive abilities that impairs the successful performance of activities of daily living. Episodic memory, the ability to recall events specific in time and place, is the cognitive function most commonly lost; 10% of persons age >70 years and 20–40% of individuals age >85 years have clinically identifiable memory loss. In addition to memory, dementia may erode other mental faculties, including language, visuospatial, praxis, calculation, judgment, and problem-solving abilities. Neuropsychiatric and social deficits also arise in many dementia syndromes, manifesting as depression, apathy, anxiety, hallucinations, delusions, agitation, insomnia, sleep disturbances, compulsions, or disinhibition. The clinical course may be slowly progressive, as in Alzheimer’s disease (AD); static, as in anoxic encephalopathy; or may fluctuate from day to day or minute to minute, as in dementia with Lewy bodies. Most patients with AD, the most prevalent form of dementia, begin with episodic memory impairment, although in other dementias, such as frontotemporal dementia, memory loss is not typically a presenting feature. Focal cerebral disorders are discussed in Chap. 22 and illustrated in a video library in Chap. 23; the pathogenesis of AD and related disorders is discussed in Chap. 35.
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FUNCTIONAL ANATOMY OF THE DEMENTIAS
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Dementia syndromes result from the disruption of specific large-scale neuronal networks; the location and severity of synaptic and neuronal loss combine to produce the clinical features (Chap. 22). Behavior, mood, and attention are modulated by ascending noradrenergic, serotonergic, and dopaminergic pathways, whereas cholinergic signaling is critical for attention and memory functions. The dementias differ in the relative neurotransmitter deficit profiles; accordingly, accurate diagnosis guides effective pharmacologic therapy.
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AD begins in the entorhinal region of the medial temporal lobe, spreads to the hippocampus, and then moves to lateral and posterior temporal and parietal neocortex, eventually causing a more widespread degeneration. Vascular dementia is associated with focal damage in a variable patchwork of cortical and subcortical regions or white matter tracts that disconnect nodes within distributed networks. In keeping with its anatomy, AD typically presents with episodic memory loss accompanied later by aphasia or navigational problems. In contrast, dementias that begin in frontal or subcortical regions, such as frontotemporal dementia (FTD) or Huntington’s disease (HD), are less likely to begin with memory problems and more likely to present with difficulties with judgment, mood, executive control, movement, and behavior.
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Lesions of frontal-striatal1 pathways produce specific and predictable effects on behavior. The dorsolateral prefrontal cortex has connections with a central band of the caudate nucleus. Lesions of either the caudate or dorsolateral prefrontal cortex, or their connecting white matter pathways, may result in executive dysfunction, manifesting as poor organization and planning, decreased cognitive flexibility, and impaired working memory. ...